This invention relates to a sewing machine with a horizontal rotary hook mechanism, and especially to a bobbin-thread supply mechanism for a sewing machine in which bobbin thread can be easily set.
In household sewing machines, horizontal rotary hook bobbin thread supply mechanisms, without a bobbin case, are replacing vertical rotary hook bobbin thread mechanisms. With the vertical rotary hook bobbin thread supply, an operator places a bobbin in a bobbin case and sets the bobbin case into the vertical rotary hook mechanism. In the horizontal rotary bobbin thread mechanisms, as shown in FIG. 9, a bobbin holder 3 includes a cylindrical container 3a below an opening 2 in a needle plate 1. In this mechanism the operator can easily put a bobbin 4 through the opening 2 into the bobbin holder 3.
In the above related art, a tension regulating portion 5 is provided for applying tension to bobbin thread drawn from the bobbin 4. The tension regulating portion 5 includes a tension bracket 6 and a tension spring 7 overlapped in an indentation 3b formed along a part of the inner periphery of the cylindrical container 3a in the bobbin holder 3, as shown in the lower part of FIG. 9. A notch 6a, only an open edge of which is shown in FIG. 9, extends obliquely from the upper edge of the tension bracket 6. When bobbin thread is passed from the notch 6a through the tension bracket 6 and the tension spring 7 to a sewing mechanism, the tension bracket 6 and the tension spring 7 apply tension to bobbin thread.
After inserting the bobbin 4 into the bobbin holder 3, the operator should pass the tip of bobbin thread drawn from the bobbin 4 through the tension regulating portion 5. Specifically, the operator should thread the notch 6a from its open edge with the tip of bobbin thread. The threading of bobbin thread is troublesome and time-consuming. If the sewing machine operates with bobbin thread being inappropriately passed through the tension regulating portion 5, excessive amount of loose bobbin thread is supplied. When bobbin thread thus differs in tension from needle thread, improper sewing results.